This invention relates to systems for underground pipe bursting and replacement.
A variety of systems are now known for the installation of underground pipes, particularly for the replacement of an existing deteriorated pipe. Pneumatic impact tools that bore horizontal holes or burst existing pipelines are in widespread use. See, for example, Wentworth et al. U.S. Pat. No. 5,025,868. In one widely practiced method, a pneumatic impact boring tool is sent through the existing pipeline such that the head of the tool, which may be provided with blades that apply intense local pressure to the existing pipe, fractures or splits the existing pipe. See, for example, Streatfield et. al. U.S. Pat. Nos. 4,720,211, 4,738,565 and 4,505,302. A replacement pipe, typically made of plastic such as HDPE, is drawn along behind the boring tool. This process has proven effective commercially because it bursts the old pipe and replaces it with a new pipe at the same time. However, exhaust from the impact tool is vented into the interior of the replacement pipe, which is unacceptable for certain types of pipe installations, such as gas and water lines.
Directional drilling machines are less effective for pipe bursting, especially for hard to burst pipes like cast iron, because the steady pushing force of the drill string lacks the impact power of a pneumatic impact boring tool. Thus, in some instances, a directional borer or winch is used to pull a pneumatic impact tool through an existing pipeline in order to burst the existing pipe and pull in the replacement pipe. These alternatives are effective but require considerable equipment and manual labor.
Wentworth U.S. Pat. No. 5,782,311 describes a pipe bursting apparatus using a directional boring machine capable of simultaneously rotating and pulling a drill string and an impact tool connectable to the drill string. The impact tool includes a tubular housing ending in a front bursting head, an input shaft, bearings supporting the input shaft for rotation within the housing, a striker disposed for reciprocation within the housing to deliver impacts to a front anvil, and a drive mechanism for simultaneously pulling the impact tool forward in response to a pulling force on the input shaft and for reciprocating the striker to drive the tool forward by the action of cyclic impacts on the front anvil. The apparatus can carry out a pipe bursting operation in a manner that eliminates the need to use a separate pneumatic impact tool to burst the existing pipe. The present invention provides an impactor which operates using a pressure fluid such as compressed air, and which can be readily used with existing directional boring machines.
A number of cable operated static bursting systems have been used for pipe bursting. Carter et al. PCT Publication WO 98/30350 describes a pipe bursting system that makes use of a relatively small, light weight hydraulic cable puller to pull a pipe bursting mole. Fisk et al. U.S. Pat. Nos. 4,983,071 and 5,078,546 describe a cable-drawn tool backed by an impact tool and provided with a blade for slitting and expanding a steel gas main. Wentworth et al. U.S. Pat. No. 6,269,889 illustrates another bursting method wherein a pneumatic tool drawn by a conventional winch is used for pipe bursting. In general systems, that rely only on static pulling force either cannot handle large pipe sizes or require a very large, powerful pulling system that is expensive and labor intensive to use. System combining pulling force with an impact tool have been able to handle larger pipe sizes than comparable static force only systems, but difficulties have been encountered with starting and stopping the tool during a run. When the tool is far down the bore, it can be difficult to re-start the tool. The present invention addresses this disadvantage among others.
An impactor of the invention for use with a directional boring machine having a drill string includes a bursting head having a rearwardly opening recess and a front end opening that communicates with the recess, an inlet pipe connected at its front end to a distal end of the drill string and extending into the recess of the bursting head through the front end opening, a striker mounted for sliding movement along the inlet pipe, a distributing mechanism responsive to pressure fluid supplied through the drill string and inlet pipe to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the bursting head, a tubular housing in which the striker and distributing mechanism are mounted, a pulling connection by which the impactor can be pulled by the drill string while the striker is delivering impacts against the head in the same direction as a pulling force exerted by the drill string, and a valve which regulates supply of pressure fluid to the distributing mechanism. The bursting head is preferably slidably mounted on the inlet pipe and moves forward relative to the inlet pipe and drill string in response to an impact of the striker against the bursting head. The tubular housing, needed to provide sealed pressure chambers, may comprise a separate tool body, an extension of the bursting head, or a front end portion of the plastic replacement pipe, as explained hereafter.
In a preferred form of the invention, a valve is provided in the inlet pipe which can shut off flow of pressure fluid, such as in response to relaxation of pulling force on the drill string that changes the relative position of the inlet tube and the bursting head. The distributing mechanism expels exhaust air rearwardly out of the tubular housing, and typically suitable means is provided for pulling the replacement pipe along behind the bursting head. For example, the replacement pipe may be secured in the rearwardly opening recess of the head, such that a front end portion of the replacement pipe forms the tubular housing.
The distributing mechanism of the impactor may be of any suitable type, but one preferred mechanism includes a rearwardly opening recess in the striker, a radial outlet hole in the striker communicating with the recess, a rear seal bearing by which the striker slidingly, sealingly engages an inner surface of the tubular housing, a radial outlet hole in the inlet pipe permitting pressure fluid to enter the rearwardly opening recess in the striker from the inlet pipe, and a sleeve mounted on the inlet pipe rearwardly of the radial outlet hole therein in sliding, sealing contact with an inner surface of the striker inside the recess, forming a rear pressure chamber in the recess ahead of the sleeve. Pressure fluid in the rear pressure chamber causes a forward stroke of the striker resulting in an impact against the bursting head, and causes the radial outlet hole in the striker to move past a front edge of the sleeve. This in turn causes pressure fluid from the rear pressure chamber to pass outwardly to a front pressure chamber outside of the striker between the striker and the tubular housing, thereby causing the striker to move rearwardly until the radial outlet hole in the striker moves past a rear edge of the sleeve. The front pressure chamber then exhausts, and a new forward stroke of the striker begins. The sleeve of the distributing mechanism may be mounted on the inlet tube, so that no rear assembly for securing the distributing mechanism to the tubular housing is needed. xe2x80x9cRadialxe2x80x9d in the context of the invention means in a direction leading outwardly from a central axis, but is not limited to a direction that is perpendicular to a central axis. A radial outlet hole could, for example, also be slanted in a lengthwise direction.
An alternative pneumatic impact mechanism according to the invention can be used to advantage in a pipe bursting impactor and can be adapted to impact tools of other types, such as underground piercing tools and jack hammers. Such a mechanism includes as general components a tubular body or housing having a rearwardly opening recess and a front end opening that communicates with the recess, an inlet pipe connectable at its front end to a source of pressure fluid and extending into the recess of the body through the front end opening, a striker mounted for sliding movement along the inlet pipe and an inside surface of the body for delivering forward impacts, the striker having a rearwardly opening recess and a front central opening of smaller diameter than the recess and which communicates with the recess, through which front opening the air inlet pipe extends, and a distributing mechanism responsive to pressure fluid supplied through the inlet pipe to cause the striker to reciprocate in a cycle. The distributing mechanism includes a radial hole in the inlet pipe permitting pressure fluid from inside the inlet pipe to enter the rearwardly opening recess in the striker, a sleeve mounted at a rear of the inlet pipe in slidable, sealing relationship with a wall of the rearwardly opening recess in the striker, forming a pressure chamber for driving the striker forwardly, a first passage for permitting pressure fluid from the rear pressure chamber to enter a front pressure chamber ahead of the striker to move the striker rearwardly after an impact, which passage is isolated from the rear pressure chamber during a part of the striker cycle in which the striker is propelled forwardly, and a second passage for exhausting the front pressure chamber after the striker has moved rearwardly a sufficient distance. Such a mechanism avoids the need for providing a radial hole through a thin tubular wall of the striker, which has been a frequent cause of breakage in xe2x80x9cstep bushingxe2x80x9d style underground piercing tools going back to Sudnishnikov et al. U.S Pat. Nos. 3,410,354 and 3,756,328.
According to another aspect of the invention, a pulling adapter is provided which can be attached to the rear end of the bursting head. The adapter has a sealing wall therein which prevents exhaust from the distributing mechanism from entering the replacement pipe, and exhaust holes permitting exhaust from the distributing mechanism to pass outside of the pulling adapter and replacement pipe. If the pulling adapter is made of plastic, it can be coaxially welded to a leading end of the replacement pipe.
The invention further provides an apparatus for use with a directional boring machine having a drill string for widening an existing hole. Such a system includes a head having a front nose portion and a rear, hole-widening portion of greater external diameter than the nose portion, and a ball joint in front of the nose portion configured for connecting the head to a drill string and permitting swiveling of the head relative to the drill string. The head may, for example, be an impactor that is pulled without rotation, or a back reamer that is rotated while being pulled to widen the existing hole. The ball joint may be provided with a passage therethrough for passing pressure fluid from the drill string to operate a pneumatic impactor. An adapter may be provided having a front end portion configured for connection to a leading end of the drill string and a mechanical coupling that connects a rear end portion of the adapter to a front end portion of the ball joint.
The invention in another aspect provides methods for replacement of an existing pipeline using a directional boring machine having a drill string and an impactor mounted at a terminal end of the drill string. In one such method, the impactor includes a bursting head, a striker which delivers impacts to the bursting head, and a pressure fluid-actuated impact mechanism. The method comprises:
(a) inserting the drill string through the pipeline;
(b) connecting a distal end of the drill string to the impactor;
(c) pulling the drill string and impactor into the pipeline while drawing a replacement pipe behind the impactor with a front end opening of the replacement pipe in a sealed condition;
(d) operating the impactor as needed to burst the pipeline by supplying a pressure fluid to operate the impactor, the pressure fluid including a lubricant; and
(e) injecting exhaust pressure fluid including the lubricant from the impactor outside the impactor and replacement pipe. A baffle or spout may be used to direct the pressure fluid rearwardly towards the replacement pipe. This both avoids contaminating the inside of the pipe with the exhaust and aids in installing the new pipe.
In another method for replacement of an existing pipeline of the invention, the pressure fluid-actuated impact mechanism has a valve regulating supply of pressure fluid to the impactor. The method includes the steps of:
(a) inserting the drill string through the pipeline;
(b) connecting a distal end of the drill string to the impactor;
(c) pulling the drill string and impactor into the pipeline while drawing a replacement pipe behind the impactor;
(d) actuating the impactor by pulling on the drill string, which causes the valve to supply pressure fluid to the impact mechanism; and
(e) stopping the impactor by reducing pulling force on the drill string. This eliminates the need to manually stop and start the impactor during bursting operation.
The invention further provides a method and apparatus for replacement of an underground pipe wherein a cable or other flexible pulling implement (such as a chain) can be used to pull the impactor. An impactor according this aspect of the invention includes a bursting head having a rearwardly opening recess, a striker mounted for sliding movement within the head, a distributing mechanism responsive to pressure fluid supplied through an inlet to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head, and a pulling connection by which the impactor can be pulled while the striker is delivering impacts against the head in the same direction as a pulling force. A length of a flexible pulling implement such as a cable is engagable to the connection at the front end of the impactor for delivering the pulling force. A cable pulling system pulls the cable in a plurality of repeated cyclic pulling strokes. Such a system includes one or more holders such as collets that engage the cable and one or more cylinders each having a movable piston operative to move the holders along the pulling stroke. In a preferred embodiment, an inlet pipe extends into the recess of the head for supplying compressed air to the distributing mechanism, and a valve in the inlet pipe shuts off flow of pressure fluid to the distributing mechanism when closed. The pulling connection may be disposed at a front end of the inlet pipe, whereby the valve is opened by pulling on the pulling connection with a pulling device and closed by relaxation of pulling force exerted by the pulling device.
A method for replacement of an underground pipe using such an apparatus includes the steps of:
(a) inserting a cable through an existing pipeline from a first end to a second end thereof;
(b) connecting a free end of the cable extending from the second end of the pipeline to an impactor, which impactor includes a bursting head having a rearwardly opening recess, a striker mounted for sliding movement within the head, a distributing mechanism responsive to pressure fluid supplied through an inlet to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head, and a pulling connection to which the cable is connected;
(c) pulling the impactor with the cable using a cable pulling system disposed at the first end of the pipeline, which cable pulling system pulls the cable in a plurality of repeated cyclic pulling strokes and includes a holder that engages the cable and a cylinder having a movable piston operative to move the holder along the pulling stroke;
(d) operating the impactor to deliver impacts against the head in the same direction as the pulling force during a cyclic pulling stroke; and
(e) reducing operation of the impactor between cyclic pulling strokes so that the impactor does not substantially move between strokes. xe2x80x9cReducingxe2x80x9d in this context means lessening the impact force delivered by the striker to the bursting head, generally by reducing the supply of compressed air or pressure fluid to the impactor partially or completely, as explained further hereafter. These and other aspects of the invention are discussed in the detailed description that follows.